The present invention relates to a refrigerant compressor, and more particularly, to a wobble plate type piston compressor for an air conditioning system in which the compressor includes a mechanism for adjusting the capacity of the compressor.
Generally, in air conditioning apparatus, thermal control is accomplished by intermittent operation of the compressor in response to a signal from a thermostat located in the room being cooled. Once the temperature in the room has been lowered to a desired temperature, the refrigerant capacity of the air conditioning system generally need not be very large in order to handle supplementary cooling due to further temperature changes in the room or for keeping the room at the desired temperature. Accordingly, after the room has cooled down to the desired temperature, the most common technique for controlling the output of the compressor is by intermittent operation of the compressor. However, intermittent operation of the compressor results in intermittent application of a relatively large load to the driving mechanism of the compressor in order to drive the compressor.
In automobile air conditioning compressors, the compressor is driven by the engine of the automobile through an electromagnetic clutch. These automobile air conditioning compressors face the same intermittent load problems described above once the passenger compartment reaches a desired temperature. Control of the compressor normally is accomplished by intermittent operation of the compressor through the electromagnetic clutch which couples the automobile engine to the compressor. Thus, the relatively large load which is required to drive the compressor is intermittently applied to the automobile engine.
Furthermore, since the compressor of an automobile air conditioner is driven by the engine of the automobile, the rotation frequency of the drive mechanism changes from moment to moment, which causes the refrigerant capacity to change in proportion to the rotation frequency of the engine. Since the capacity of the evaporator and condenser of the air conditioner does not change when the compressor is driven at high rotation speed, the compressor performs useless work. To avoid performing useless work, prior art automobile air conditioning compressors often are controlled by intermittent operation of the magnetic clutch. Again, this results in a large load being intermittently applied to the automobile engine.
Recently, it was recognized that it is desirable to provide a wobble plate type piston compressor with a displacement or capacity adjusting mechanism to control the compression ratio in response to demand. In a wobble plate type piston compressor, control of the compression ratio can be accomplished by changing the slant angle of the sloping surface of the slant plate in response to operation of the valve control mechanism as disclosed in U.S. Pat. No. 4,586,874 issued May 6, 1986 to Masaharu Hiraga et al. Referring to FIG. 8, this application discloses a mechanism for controlling the compression ratio of the compressor which includes a passageway 391 formed between suction chamber 35 and crank chamber 13. This passageway 391 is formed by drilling a hole through cylinder block 101 and valve plate 24. The machining operation required to form the passageway 391 adds to the manufacturing cost of the compressor. Furthermore, the formation of passageway 391 through cylinder block 101 tends to decrease the mechanical strength and structural integrity of cylinder block 101. The mechanical strength and structural integrity of the cylinder block in a wobble plate type compressor is of considerable importance due to the high pressures which are present inside the cylinder block during operation of the compressor. Thus, in order to maintain the requisite strength and integrity, the diameter of the cylinder block 101 must be enlarged, further adding to manufacturing cost, weight and overall size of the compressor.